1. Field of the Invention
This invention relates to a treatment of industrial process wastewater, and more particularly concerns a process and a process wastewater treatment plant for converting sulfuric acid based process wastewater generated in industry, such as process wastewater generated during the manufacturing and recycling of lead-acid batteries, into (a) sodium sulfate salt and (b) clean water for reuse as process water.
2. Description of the Prior Art
Manufacturing plants, such as plants that manufacture lead-acid batteries and which may recycle scrap lead-acid batteries, generate large quantities of process wastewater from the process water used during manufacturing operations. Typically, such wastewater is disposed of by discharging it into the environment, i.e., into streams and rivers, and because such wastewater contains hazardous and residual waste generated during manufacturing operations, the law requires that the wastewater be treated to remove hazardous and residual waste before the water is discharged into the environment.
Historically, wastewater treatment has presented a challenge for the battery manufacturing industry as well as other metals related industries. It has been difficult or not feasible to remove sufficient quantities of heavy metals, sulfates, and dissolved solids from the wastewater to meet today's strict environmental standards.
Treatment of the wastewater using "Best Available Technology" (BAT) criteria, as currently defined by the Environmental Protection Agency (EPA) for wastewater treatment in the battery manufacturing and other metals related industries, produces a treated wastewater effluent containing high concentrations of dissolved solids (i.e., calcium sulfate) and residual trace concentrations of metals and other inorganics. The calcium sulfate typically is present in concentrations high enough (6,000 to 9,000 ppm (parts per million) to be a potential risk of creating a negative impact on aquatic organisms and drinking water quality. This conventional technology also produces a significant volume of sludge designated as hazardous due to its metals content. The sludge requires further treatment and then disposal, i.e., usually in a landfill.
Further, in metals related industries, large quantities of water are used daily during manufacturing operations. For example, in the lead-acid battery manufacturing industry, hundreds of thousands of gallons of wastewater may be generated each day. Under current practice, this wastewater is first treated, which is costly, before it is discharged into the environment. Over the course of a year, millions of gallons of fresh process water must be obtained since the process wastewater is not recycled, which results in added costs and possible depletion of ground water supplies.